In general, the fractional flow reserve (FFR) is widely used as a clinical indicator for evaluating the functional severity of coronary artery stenosis. A computer simulation method based on computed tomography (CT) data of a patient is a non-invasive method for calculating the FFR. This method can provide a detailed analysis result to the hemodynamics of a stenosed coronary artery by combining a computational fluid dynamics model with a lumped parameter model of a cardiovascular system.
Pijls et al. have introduced, as an indicator of a coronary artery disease, the fractional flow reserve (FFR) which refers to a ratio of a micro-vessel having a completely expanded state and a micro-vessel having a stenosed state. Pijls et al. have showed a method of measuring the FFR using a guide wire technique, which became a technique of evaluating the degree of stenosis of a coronary artery.
Kim et al. has presented a non-invasive simulation method which takes advantage of a CT image and patient information when evaluating an FFR value. This is a method in which a computational fluid dynamics technique for hemodynamic calculation of an aorta and a coronary vessel is combined with a lumped parameter model of the whole cardiovascular system. The validity and usefulness of this simulation model has been verified through several studies (Min et al., 2012; Koo et al., 2011). However, the model developed by Kim et al. requires complex calculation and identification of many parameters, consequently increasing the uncertainty of simulation, because the aorta is included in the computational fluid dynamics model and because the whole cardiovascular system is included in the lumped parameter model.
Korean Patent No. 10-1524955 (entitled: patient-specific blood flow modeling method and system) discloses a method and system for determining cardiovascular information of a patient. The cardiovascular information determining method disclosed in the above patent includes the steps of: receiving a patient-specific data on the geometry of an anatomical structure of a patient including at least a part of a plurality of coronary arteries originating from an aorta; generating a three-dimensional model indicating a first part of the anatomical structure of the patient including at least a part of the plurality of coronary arteries based on the patient-specific data; generating a physics-based model on blood flow characteristics in the first part of the anatomical structure at least partially based on a mass or volume of myocardial tissue; and determining a fractional flow reserve in the first part of the anatomical structure based on the three-dimensional model and the physics-based model.
In the method disclosed in the above patent, the physics-based model makes use of a lumped parameter model which indicates blood flow through the boundary of the three-dimensional model. In the case of using the lumped parameter model, a blood flow rate condition is set based on the volume of a ventricular muscle. This is based on the assumption that the blood flow rate grows larger in a region having a larger volume of a ventricular muscle among the regions to which blood is supplied by coronary arteries. In the method disclosed in the above patent, it is necessary to find the volume of myocardial tissue and to use a scaling law. In order to use the scaling law, it is essential to perform segmentation of a three-dimensional ventricular model. That is to say, a segmentation work for the entirety of the heart needs to be carried out in order to apply the method of the above patent. Thus, the uncertainty of the model increases. In particular, the ventricular muscle has a complex shape in the thickness direction. This may reduce the accuracy of segmentation.
In the method developed by Kim et al. and the method disclosed in the above patent, an aorta is included in the computational fluid dynamics model (hereinafter referred to as a “CFD model”). The lumped parameter model is composed of a closed circuit including a body artery, a body vein, a pulmonary vein, a left heart, a right heart and the like. For the sake of hemodynamics analysis, the CFD model and the lumped parameter model make use of parameters having some standard representative values. Such parameters (e.g., resistance values and capacitance values for a body artery, a body vein, a pulmonary vein and the like) are not suitable for application to individual patients.